The present invention relates to a pump comprising a housing and a pump unit arranged therein, the pump unit comprising a first and a second thrust plate and a ring arranged therebetween and having a through opening, at least at an outer peripheral region of the ring resting on the two thrust plates, a pressure chamber being formed between the second thrust plate and the housing.
Pumps of the type described above are known. The pump is provided with a housing which receives a pump unit. The pump unit comprises a first and a second thrust plate, between which a ring is arranged. A pump chamber is thus formed in which a pump insert is arranged which comprises movable parts for drawing in and compressing a medium. During operation of the pump the movable parts of the pump insert are moved along the inside of the ring and/or the thrust plates. It has been found that the compressed medium deforms the thrust plates. In particular, the thrust plates bulge outwards. A gap is thus formed between the movable parts of the pump insert and the thrust plates. As a result, a shortcircuit is effectively produced between the pressure region and the suction region of the pump, so that the medium conveyed can flow out of the pressure region into the suction region. This has an adverse effect upon the volumetric efficiency of the pump.
In order to improve the efficiency of such a pump, the side of one thrust plate remote from the pump chamber is acted upon with the fluid pressure from the pressure region. The other thrust plate is supported on a face of the housing. That face of the housing has to be made particularly flat so that the thrust plate rests uniformly thereon. In this case the housing is formed by a cup-shaped housing half and by a plane housing lid which is provided with the flat face. A disadvantage of this is that the flat face of the lid can be produced only at a substantial cost. In addition, the entire housing, and in particular the lid, has to be constructed with a particularly high degree of rigidity, so that it can act as an abutment for the thrust plate.
In other known pumps, in order to improve efficiency, the side of the two thrust plates remote from the pump chamber is acted upon with the fluid pressure from the pressure region. This has the disadvantage that an additional cost for sealing is required in order to be able to supply the thrust plates from outside with the medium acted upon with pressure.